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It all ADs up: Boosting food waste supply to anaerobic digestion

Anaerobic digestion capacity in the UK continues to rise, but the proportion of food waste among feedstocks is falling. Resource asks how a boost in collections might impact the AD sector?

The UK has an EU-mandated target of 50 per cent municipal recycling by 2020, a goal that it currently seems unlikely to hit. In the next three years a gap of about five per cent has to be filled, with even greater EU targets for 2030 likely to precede Brexit. Food waste holds the key.

Speaking at the Resourcing the Future conference this summer, WRAP’s Linda Crichton explained that to get where we need to be, the UK will have to recycle some 1.6 million tonnes more, and while there is of course potential to provide this with improved and more comprehensive dry recycling, her presentation suggested that new food collections could add nearly as much as those and the maximisation of current food waste collections combined.

As well as taking the next step in recycling improvement and pulling us up to speed with our targets, new food waste collections would fill the growing need to feed the anaerobic digestion (AD) plants popping up around the UK.

The UK now has 557 AD plants operating at a capacity of 730 MWe-e, an increase of 18 per cent over the same period in 2016, according to Anaerobic Digestion & Bioresources Association’s (ADBA) latest market report, published in July. That network is generating 10.7 TWh per year – enough, the organisation says, to power over a million homes. But while we might think of these plants as turning our food waste into green energy, 292 of them still feed off purpose-grown crops and the proportion of plants being fed by food waste is dropping.

The amount of food waste being used in AD plants is still rising, but at a much-slowed rate – 2.3 million tonnes (mt) is currently recycled through AD, up from 2.1mt last year. This is on a similar level to farm waste (2.1mt) and crops (2.4mt). Industrial residues contribute 6.2mt, liquid effluents from food and drink processing a further 6mt, and the organic fraction of residual waste an estimated 0.8mt (all figures from ADBA’s report). This means that food waste only contributes 16.6 per cent of the material being taken to AD plants, and that’s before the 24 million tonnes of sewage sludge reported by ADBA is included (84 per cent of all sewage sludge is now processed through AD).

In the last few years, the number of plants taking agricultural waste has rocketed, rising from 47 in 2012 to 265 in 2016. The growth of municipal and commercial food waste AD plants however has slowed, with only seven added last year. These types of plants now account for under 20 per cent of the total number of plants in the planning process. ADBA attributes this to issues with food waste availability and falling gate fees.

The report says that household and business municipal food waste is becoming ‘increasingly scarce’ for AD, and that the increase in food waste tonnage is expected to continue slowing. But this isn’t because the material isn’t there. WRAP figures suggest that an estimated 10mt of post-farm gate food is wasted across the UK every year, yet only 1.8mt is currently recycled, and half a million of those are the result of home composting. So why are some AD facilities having to take virgin crops to keep their plants running at capacity?

In the UK, 50 per cent of households receive no local authority food waste service, and of the half that do, only 31 per cent have access to separate weekly food waste collections, with the rest made to throw it in with their garden waste. In England, of the 4.6 million tonnes of food waste that actually is collected each year by local authorities, only 12 per cent actually gets recycled.

Charlotte Morton, Chief Executive at ADBA, says that mandatory separate food collections is the only way to get this waste treated properly: “Mandatory separate collections in Scotland, Wales, and Northern Ireland have all seen a rise in the amount of food waste recycled and a fall in the amount of food wasted. They are the only way of ensuring that the nearly 8.5 million tonnes of unavoidable and inedible food waste that should be recycled can go to AD plants.”

Since January 2016 it has been compulsory for Scottish food businesses to separate it out for collection, and businesses producing more than 50kg a week have been doing so since 2014. It also became mandatory for councils in non-rural areas to collect separate food waste. Northern Ireland has followed Scotland’s model by making 50kg a week businesses separate their food waste from April 2016, and from this April all councils have had to provide a container for separate food waste collection. In Wales almost 100 per cent of households already receive household food waste collections.

Yet even in Wales, where nigh-on 100 per cent of the homes are reached by council food waste collections, more than a third of residual waste (33.6 per cent, to be exact) is made up of organic matter, according to a WRAP Cymru study from last year, of which at least 16 per cent is food waste. Faced with these figures, more and more councils, particularly in Wales and Scotland, but also Greater Manchester, are pushing this material into the food waste stream by restricting residual capacity, either through slim bins or reduced frequency of collections. Bury, the first council in England to go three-weekly, collected an extra 1,349 tonnes of organic waste in the first year after the switch, with another rise of 1,153 tonnes the year after that.

To try and press the issue, WRAP last year published the Food Waste Recycling Action Plan for England, an industry-wide project designed to increase the amount of food waste being collected from households and the commercial and industrial sector, and share the costs and benefits of collection, while, critically, providing long-term sustainable feedstocks for operators of recycling plants.

Putting in place long-term solutions to increase the amount of food waste being recycled would add a degree of certainty that would have great impacts on the AD market, says Morton: “This in turn would likely lead to more food-waste AD plants being built as contracts for food-waste feedstocks would be more secure and banks would subsequently be more likely to lend money to such projects. This level of certainty is critical for food-waste AD plants in particular as planning permission for these types of plant is stricter than for other types of AD plant.”

One such plant, ReFood’s new Dagenham facility, is capable of processing more than 160,000 tonnes of food waste every year. The East London plant, which opened in July, hopes to capitalise on the huge commercial food waste production in the capital. “Animal manures and crops such as maize can be used in a similar manner to generate green energy: it is believed that around 30 per cent of UK maize yield is now being used as a feedstock for AD plants,” says Philip Simpson, ReFood’s Commercial Director. “Using prime agricultural land to produce energy crops while allowing the landfilling of a far more suitable feedstock like food waste is not sustainable. In terms of the potential for converting food waste to energy, the current volume of food waste being landfilled would support over 80 plants similar to Dagenham and produce enough biomethane for more than one million homes.”

While Morton agrees that food waste can provide a sustainable base for AD, she refutes the fact that crop use for feedstock is an issue. “It’s important to keep the size of these operations in context,” she says. “Growing crops for AD in the very highest scenarios would still only use under one per cent of the UK’s agricultural land. The growing of crops as part of an agricultural rotation is a proven farming method, used to improve soil quality and food production yields and to reduce the need for pesticides.”

Further, Morton maintains it is not a case of AD plants using virgin crops to make up for a lack of food waste available. “AD plants that use purpose-grown energy crops as a feedstock usually do so as part of a pre-prepared feedstock plan, often alongside farm wastes like slurries and crop offcuts. AD plants intending to use purpose-grown energy crops as a feedstock have to design in the relevant facilities and equipment (such as silage clamps) from the beginning, meaning that AD plants not designed to do this generally cannot make up shortfalls in feedstock using crops on an ad-hoc basis.”

In the meantime, the need for material for food waste AD plants and competition between operators is driving down gate fees. According to WRAP’s annual Gate Fee report, the median gate fee for AD in 2016 was £29 per tonne, compared with £40 per tonne in 2015. “We aren’t expecting a resurgence in gate fees,” admits Morton, “though market forces are difficult to predict. This will depend on the demand for food waste treatment capacity (determined by producers and government policy) and the ‘supply’ provided by AD operators (new plants putting downward pressure on gate fees). We don’t expect a dramatic decline in fees, but we certainly don’t expect an increase.”

While the low fee isn’t good for operators, it does make food waste disposal an attractive proposition for producers at a time that costs of residual disposal is continuing to rise. Crichton explains: “Our work with local authorities suggests that a lower gate fee improves the case for treating food waste by AD compared to disposing of it via landfill or incineration. However, the extent to which it helps make collections more cost effective will depend in part on local arrangements for sharing this benefit between disposal and collection authorities.”

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